content: /*
   * Copyright 2016-present David Karnok
   *
   * Licensed under the Apache License, Version 2.0 (the "License");
   * you may not use this file except in compliance with the License.
   * You may obtain a copy of the License at
   *
   *     http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  
  package hu.akarnokd.rxjava3.operators;
  
  import java.util.Iterator;
  import java.util.concurrent.atomic.*;
  
  import org.reactivestreams.*;
  
  import io.reactivex.rxjava3.core.*;
  import io.reactivex.rxjava3.exceptions.Exceptions;
  import io.reactivex.rxjava3.internal.subscriptions.*;
  import io.reactivex.rxjava3.internal.util.BackpressureHelper;
  
  final class FlowableSwitchIfEmptyMany<T> extends Flowable<T>
  implements FlowableTransformer<T, T> {
  
      final Flowable<T> source;
  
      final Iterable<? extends Publisher<? extends T>> alternatives;
  
      FlowableSwitchIfEmptyMany(Flowable<T> source, Iterable<? extends Publisher<? extends T>> alternatives) {
          this.source = source;
          this.alternatives = alternatives;
      }
  
      @Override
      protected void subscribeActual(Subscriber<? super T> s) {
          Iterator<? extends Publisher<? extends T>> it;
          try {
              it = alternatives.iterator();
          } catch (Throwable ex) {
              Exceptions.throwIfFatal(ex);
              EmptySubscription.error(ex, s);
              return;
          }
          SwitchManySubscriber<T> parent = new SwitchManySubscriber<>(s, it);
          s.onSubscribe(parent);
          parent.drain(source);
      }
  
      @Override
      public Publisher<T> apply(Flowable<T> upstream) {
          return new FlowableSwitchIfEmptyMany<>(upstream, alternatives);
      }
  
      static final class SwitchManySubscriber<T>
      extends AtomicInteger
      implements Subscriber<T>, Subscription {
  
          private static final long serialVersionUID = -174718617614474267L;
  
          final Subscriber<? super T> downstream;
  
          final AtomicLong requested;
  
          final AtomicReference<Subscription> upstream;
  
          final Iterator<? extends Publisher<? extends T>> alternatives;
  
          boolean hasValue;
  
          volatile boolean active;
  
          SwitchManySubscriber(Subscriber<? super T> downstream, Iterator<? extends Publisher<? extends T>> alternatives) {
              this.downstream = downstream;
              this.alternatives = alternatives;
              this.requested = new AtomicLong();
              this.upstream = new AtomicReference<>();
          }
  
          @Override
          public void request(long n) {
              if (SubscriptionHelper.validate(n)) {
                  BackpressureHelper.add(requested, n);
                  Subscription a = upstream.get();
                  if (a != null) {
                      a.request(n);
                  }
              }
          }
  
          @Override
          public void cancel() {
              SubscriptionHelper.cancel(upstream);
          }
  
          @Override
          public void onSubscribe(Subscription s) {
              if (SubscriptionHelper.replace(this.upstream, s)) {
                  long n = requested.get();
                  if (n != 0L) {
                      s.request(n);
                  }
              }
          }
  
          @Override
          public void onNext(T t) {
              if (!hasValue) {
                  hasValue = true;
              }
              downstream.onNext(t);
          }
  
          @Override
          public void onError(Throwable t) {
              downstream.onError(t);
          }
  
          @Override
          public void onComplete() {
              if (hasValue) {
                  downstream.onComplete();
              } else {
                  active = false;
                  drain(null);
              }
          }
  
          void drain(Publisher<? extends T> source) {
              if (getAndIncrement() == 0) {
                  do {
                      if (SubscriptionHelper.CANCELLED == upstream.get()) {
                          return;
                      }
  
                      if (!active) {
                          if (source == null) {
                              boolean b;
                              try {
                                  b = alternatives.hasNext();
                                  if (b) {
                                      source = alternatives.next();
                                  }
                              } catch (Throwable ex) {
                                  Exceptions.throwIfFatal(ex);
                                  downstream.onError(ex);
                                  return;
                              }
  
                              if (!b) {
                                  downstream.onComplete();
                                  return;
                              }
                              if (source == null) {
                                  downstream.onError(new NullPointerException("The alternative Publisher is null"));
                                  return;
                              }
                          }
                          active = true;
                          source.subscribe(this);
                          source = null;
                      }
                  } while (decrementAndGet() != 0);
              }
          }
      }
  }
  